1. Field of the Invention
The present invention relates generally to wireless networks, and more specifically, to a radio-frequency identification tag and system for determining the physical location of tagged items.
2. Background of the Invention
Radio-frequency identification (RFID) tags are becoming widespread for locating items such as store inventory and corporate assets, as well as for employee locating via RFID badges. Locating stations are typically part of a dedicated wireless system for receiving tag signals from the RFID tags. Reception information is gathered from multiple location stations and the location of the RFID tags is determined at a central master station.
Wireless local area networks (WLANs) have also become widespread. WLANs according to the Institute of Electrical and Electronic Engineers (IEEE) specifications 802.11 (WLAN) (including 802.11a, 802.11b, etc.), 802.15.1 (WPAN) and 802.15.4 (WPAN-LR) provide wireless interconnection of computing devices and personal communications devices, as well as other devices such as home automation devices. Combinations of RFID tag systems and WLAN systems are available, but the RFID tags currently marketed use frequency bands and/or signaling mechanisms separate from the wireless local networks. The use of separate bands and/or signaling mechanisms requires substantial additional hardware in the locating stations for receiving signals that are intermittently transmitted from the tags at predetermined intervals. The additional hardware increases the cost and complexity of the locating stations.
Location finding within WLANs using signaling on a WLAN channel has been developed for WLAN units as described in the above-incorporated patent application: “METHOD AND SYSTEM FOR LOCATION FINDING IN A WIRELESS LOCAL AREA NETWORK”. However, the complexity of a full WLAN unit including a network receiver, full MAC (Medium Access Control) support and interface is not justified for some applications in which a low-cost RFID tag is desirable. For example, employee badges and inventory tags do not require a full WLAN unit including a full receiver, transmitter and network support that generally will not be cost-justified for these applications.
Therefore, it would be desirable to provide an improved method and system for implementing RFID tag location finding in a wireless network, so that the physical location of tagged items may be determined by the wireless network without requiring substantial additional or special hardware in the locating stations or tags. It would also be desirable to provide such improved method and system without requiring the use of an additional frequency band. It would further be desirable to provide a wireless network including location units where both tags and standard units may be located by the same location units.